The present invention is applicable to a variety of IMDs utilizing pulse generators to stimulate selected body tissue. However, in this instance, the invention and its background will be described principally in the context of a specific example of such devices, namely, an implantable cardiac pacemaker and defibrillator unit having a connector assembly defining multiple lead-receiving receptacles. The appended claims are not intended to be limited, however, to any specific example or embodiment described herein.
Cardiac pacemakers, and other implantable stimulation devices such as cardioverters and defibrillators, are hermetically sealed within a housing or casing (sometimes also referred to as a “can”) to isolate the electronic circuits contained within the device from the body environment. Such devices require that electrical signals be reliably passed between the hermetically sealed circuitry and external connectors without compromising the hermeticity of the device. Depending on the configuration of the implantable device there may be multiple electrical paths required between the device and its external connectors for delivering, for example, multi-chamber or multi-site stimulation and shock therapy, and for receiving sensed cardiac signals. These paths must be electrically and mechanically integrated with the device to provide a safe, long-term connector assembly that does not compromise the hermetic package.
Typically, a hermetic housing feedthrough electrically couples the electronic circuits contained within the device housing or casing to the connector assembly. The feedthrough extends through the wall of the hermetically sealed casing into the connector assembly so as to couple the electronic circuits within the casing to lead-receiving receptacles within the connector assembly. Each lead has one or more electrical terminals on a proximal end thereof, typically in the form of a pin terminal and one or more conductive ring terminals. Typically, the pin is electrically coupled to a distal tip electrode and is therefore sometimes called the “tip terminal.” When the proximal end of the lead is inserted into the lead receptacle of a connector assembly, contacts within the receptacle come into contact with corresponding terminals on the lead so as to couple the lead to the electronic circuits within the implantable stimulation device via the feedthrough assembly. Needless to say, it is imperative that a completely dependable electrical connection be made and retained between the lead terminals and the corresponding connector assembly contacts. At the same time, the connector assembly must be capable of releasing the lead from the lead receptacle during explantation or other subsequent surgical procedure, and must also tightly seal against the entry of body fluids.
It is known in prior art connector assemblies to electrically and mechanically connect the proximal end of the lead within a receptacle of the connector assembly by means of a variety of expedients including captive fastening screw/collet arrangements and setscrews. In those prior art connector assemblies in which the lead is fixed within the lead receptacle using a setscrew, the setscrew is often threaded into an electrical connector block within the connector assembly. When the screw is advanced, it comes into contact with an associated terminal on the proximal end of the lead, mechanically and electrically coupling the lead and the connector assembly. However, the proximal end of a lead is sometimes damaged by an over-tightened setscrew and setscrews have a history of stripping out of the threaded connector block. To minimize or eliminate such problems, setscrews of a certain minimum physical size have been employed. The result is often a protrusion on the side of the connector assembly as the physical size of the pacemaker and its connector assembly is reduced.
A further problem of prior art setscrew type connector assemblies arises from the need to isolate the setscrew and the setscrew block from body fluids. One solution has been to use a silicone seal called a septum. The septum forms an insulation barrier between the setscrew and body fluids. However, the septum must permit a wrench to pass through it so that the screw can be tightened. Frequently, the septum is damaged by the wrench resulting in a loss of the insulation barrier.
One improvement is disclosed in U.S. Pat. No. 4,934,366 to Truex et al. which provides a feedthrough connector for a pacemaker, or other implantable medical device, that advantageously combines the connector function with the feedthrough function and eliminates the need for the cast epoxy connector previously used on prior art pacemakers. According to the Truex et al. patent, eliminating the external cast epoxy connector advantageously eliminates the need for septums, setscrews, and the feedthrough terminal and its associated platinum wires and connector blocks, as well as the whole time consuming casting process with its inherent propensity for cosmetic problems. In this patented instance, the feedthrough/connector includes a barrel assembly having an open end and a closed end. The open end of the assembly provides an opening into which the connecting end of a pacemaker lead, or other electrical lead, can be inserted. The barrel assembly includes metal (conductive) portions separated by ceramic (nonconductive) insulating portions. An overlap region of the conductive portions, separated by the nonconductive portion, advantageously provides structural strength as well as a capacitor structure which helps filter out unwanted electromagnetic interference (EMI) signals from passing through the connector. Spring contacts are mounted on the inside of the metal portions and are adapted to make electrical contact with the appropriate electrodes of the pacemaker or other electrical lead when the connecting end of the lead is inserted into the connector.
Another known improvement is disclosed in U.S. Pat. No. 5,252,090 to Giurtino et al. which discloses a connector assembly for an implantable stimulating device which employs a lead-locking spring clip to reliably provide a mechanical and electrical connection between the terminal pin of an electrode lead and the device, while reducing the user interaction required during implantation and disconnection. In this patented instance, no tools are required to establish the connection, nor is user action, other than inserting the lead into the connector, necessary to lock the lead into place. Disconnecting the lead requires only the application of a modest transverse compressing force to a release button on the connector assembly. In the event that a withdrawal force is applied to the lead without simultaneously applying the compressing force to the release button, the connector assembly increases its holding force on the electrode lead.
U.S. Pat. No. 5,951,595 to Moberg et al. discloses a connector assembly mounted on an implantable cardiac stimulation device having a side-actuated mechanism for fixing and tightly sealing electrical leads inserted into lead receptacles within an IMD connector assembly without the use of setscrews. In the Moberg et al. patent, fixing and sealing of the leads is accomplished by compressing resilient lead lock O-ring seals, disposed in annular recesses, with lip portions of a plunger drawn toward a molded support by the actuator mechanism.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.